1. Field of the Invention
This invention relates to a sheet processing apparatus and, more particularly, to a sheet processing apparatus sequentially fetching inside sheets such as copy papers conveyed from an image forming apparatus such as photocopiers, printers, facsimile machines, and the like and executing selectively operations such as folding, sorting, stapling, and so of to the sheets.
2. Description of Related Art
Image forming apparatuses such as photocopiers are conventionally structured, for rendering easy processing work such as photocopying, to have an original document automatic feeding apparatus for feeding automatically original documents and a sheet processing apparatus such as, a so-called finisher and stitcher for selectively doing operations such as sorting operation for arranging or classifying sheets on which images are formed, a staple operation for selectively stapling a bundle made of plural sheets, a folding operation for selectively folding a bundle made of plural sheets, a stack operation for stacking the sheets or sheet bundles in stacking them, and so on. An image forming apparatus is constituted by connecting with those apparatuses.
The sheet processing apparatus has a rocking guide rocked by a drive mechanism composed of a motor and a gear series, and the rocking guide has a pulling means rotatively provided for pulling in a direction opposite to the delivery direction the delivered sheets on the temporarily stacking tray for temporarily stacking sheets. The pulling means rotates in a direction opposite to the sheet delivery direction at every delivery of a single sheet on the temporarily stacking means, is transformed elastically when contacting with the rear end of the sheets on the temporarily stacking means, and pulls back the sheets by the frictional force created between the sheet and the means.
However, if the pulling means pulls back the sheets at every sheet delivery while the rocking guide is held at a fixed position upon rocking in a separating direction from the temporarily stacking means, the sheet height of the topmost sheet on the temporarily stacking means changes because the sheets are delivered one by one on the temporarily stacking means, and therefore, the contact area and contact pressure of the pulling means in contact with the topmost sheet are changed, thereby possibly causing over returning of the sheets.
It is an object of the invention to provide a sheet processing apparatus to prevent the sheets from being excessively returned due to changes of the contact area and contact pressure of the pulling means with respect to the topmost sheet on the temporarily stacking means.